Spray foams have found widespread utility in the fields of insulation and structural reinforcement. For example, spray foams are commonly used to insulate or impart structural strength to items such as automobiles, hot tubs, refrigerators, boats, and building structures. In addition, spray foams are used in applications such as cushioning for furniture and bedding, padding for underlying carpets, acoustic materials, textile laminates, and energy absorbing materials. Currently, spray foams, especially those used as insulators or sealants for home walls, are polyurethane spray foams.
Polyurethane spray foams and their methods of manufacture are well known. Typically, polyurethane spray foams are formed from two separate components, commonly referred to as an “A” side and a “B” side, that react when they come into contact with each other. The first component, or the “A” side, contains an isocyanate such as a di- or poly-isocyanate that has a high percent of NCO (nitrogen, carbon and oxygen) functional groups on the molecule. The second component, or “B” side, contains nucleophilic reagents such as polyols that include two or more hydroxyl groups, silicone-based surfactants, blowing agents, catalysts, and/or other auxiliary agents. The nucleophilic reagents are generally polyols, primary and secondary polyamines, and/or water. Preferably, mixtures of diols and triols are used to achieve the desired foaming properties. The overall polyol hydroxyl number is designed to achieve a 1:1 ratio of first component to second component (A:B).
The two components are typically delivered through separate lines into a spray gun such as an impingement-type spray gun. The first and second components are pumped through small orifices at high pressure to form separate streams of the individual components. The streams of the first and second components intersect and mix with each other within the gun and begin to react. The heat of the reaction causes the temperature of the reactants in the first and second components to increase. This rise in temperature causes the blowing agent located in the second component (the “B” side) to vaporize and form a foam mixture. As the mixture leaves the gun, the mixture contacts a surface, sticks to it, and continues to react until the isocyanate groups have completely reacted. The resulting resistance to heat transfer, or R-value, may be from 3.5 to 8 per inch.
There are several problems associated with conventional polyurethane spray foams. For example, although sealing a building with such polyurethane spray foams reduces drafts and keeps conditioned air inside and external air outside of a building, there is a reduction in the ability of moisture to penetrate the building. As a result, the levels of moisture and air pollutants rise in these tightly sealed buildings that no longer permit moisture penetration into the building.
Another problem associated with conventional polyurethane spray foams is that the first component (the “A” side) contains high levels of methylene-diphenyl-di-isocyanate (MDI) monomers. When the foam reactants are sprayed, the MDI monomers form droplets that may be inhaled by workers installing the foam if stringent safety precautions are not followed. Even a brief exposure to isocyanate monomers may cause difficulty in breathing, skin irritation, blistering and/or irritation to the nose, throat, and lungs. Extended exposure of these monomers can lead to a sensitization of the airways, which may result in an asthmatic-like reaction and possibly death.
An additional problem with such conventional polyurethane spray foams is that residual polymeric methylene-diphenyl-di-isocyanate (PMDI) that is not used is considered to be a hazardous waste. PMDI typically has an NCO of about 20%. In addition, PMDI can remain in a liquid state in the environment for years. Therefore, specific procedures must be followed to ensure that the PMDI waste product is properly and safely disposed of in a licensed land fill. Such precautions are both costly and time consuming.
In this regard, attempts have been made to reduce or eliminate the presence of isocyanate and/or isocyanate emission by spray foams into the atmosphere. Examples of such attempts are set forth below.
U.S. Patent Publication No. 2006/0047010 to O'Leary teaches a spray polyurethane foam that is formed by reacting an isocyanate prepolymer composition with an isocyanate reactive composition that is encapsulated in a long-chain, inert polymer composition. The isocyanate prepolymer composition contains less than about 1 wt % free isocyanate monomers, a blowing agent, and a surfactant. The isocyanate reactive composition contains a polyol or a mixture of polyols that will react with the isocyanate groups and a catalyst. During application, the spray gun heats the polymer matrix, which releases the polyols and catalyst from the encapsulating material. The polyols subsequently react with the isocyanate prepolymer to form a polyurethane foam.
U.S. Pat. No. 7,053,131 to Ko, et al. discloses absorbent articles that include super critical fluid treated foams. In particular, super critical carbon dioxide is used to generate foams that assertedly have improved physical and interfacial properties.
U.S. Pat. No. 6,753,355 to Stollmaier, et al. discloses a composition for preparing a latex foam that includes a latex and a polynitrilic oxide (e.g., 2,4,6-triethylbenzene-1,3-dinitrile oxide) or a latex and an epoxy silane. The latex may be carboxylated. It is asserted that the composition is stable for at least twelve months and that the one-part coating systems can be cured at room temperature without the release of by-products.
U.S. Pat. No. 6,414,044 to Taylor teaches foamed caulk and sealant compositions that include a latex emulsion and a liquid gaseous propellant component. The foamed compositions do not contain a gaseous coagulating component.
U.S. Pat. No. 6,071,580 to Bland, et al. discloses an absorbent, extruded thermoplastic foam made with blowing agents that include carbon dioxide. The foam is allegedly capable of absorbing liquid at about 50 percent or more of its theoretical volume capacity.
U.S. Pat. No. 5,741,823 to Hsu teaches producing a smooth, hard coating on a wood substrate. The coating is made of a foamed, polymerized latex emulsion and is applied on the surface of a wood substrate.
U.S. Pat. No. 5,585,412 to Natoli, et al. discloses a process for preparing flexible CFC-free polyurethane foams that uses an encapsulated blowing agent. The process provides a polyurethane foam having a desired density that avoids the use of chlorofluorocarbons or other volatile organic blowing agents. The encapsulated blowing agent assertedly supplements the primary blowing action provided by water in the manufacture of water-blown polyurethane foam and facilitates in the production of foam having the desired density.
U.S. Pat. No. 4,306,548 to Cogliano discloses lightweight foamed porous casts. To manufacture the casts, expanded non-porous polystyrene foam beads or other shapes are coated with a layer of neoprene, natural rubber, or other latex. The coated polystyrene is then encased in a porous envelope, and the envelope is applied to a broken limb. Additional coated polystyrene is added over the envelope and a gaseous coagulant is added to gel the latex, which causes the polystyrene beads to adhere to each other and produce a unified, rigid structure.
Despite these attempts to reduce or eliminate the use of isocyanate in spray foams and/or reduce isocyanate emission into the air, there remains a need in the art for a spray foam that is non-toxic and environmentally friendly.